The present invention generally relates to systems for obtaining synchronized reproduction from a plurality of reproducing apparatuses, and more particularly to a system for synchronously reproducing digital signals recorded together with address signals, by respectively obtaining synchronism with respect to a plurality of recording and reproducing apparatuses.
Conventionally, for example, a digital signal such as a pulse-code-modulated (PCM) audio signal has been recorded instead of a video signal, by use of a magnetic recording and reproducing apparatus (so-called VTR) which records and reproduces a video signal with respect to a magnetic tape by rotary heads. In this system, a two-channel signal, that is, the right-channel signal and the left-channel signal, are subjected to time-division multiplexing and recorded in each track.
When signals of three or more channels are to be recorded and reproduced, for example, in a case where signals of four-channels are to be recorded and reproduced, a method can be considered in which a plurality of, for example, two recording and reproducing apparatuses are synchronously operated to perform recording and reproduction in a state where the two apparatuses are mutally in synchronism.
Accordingly, the present inventors have devised and tested the following system. In this system, two recording and reproducing apparatuses are synchronously operated by use of a synchronizing signal. Several hundred words of digital data are designated by one block, and an address signal is added to each block. A first-channel signal and a second-channel signal are recorded on the magnetic tape by one recording and reproducing apparatus, and a third-channel signal and a fourth-channel signal are recorded on the magnetic tape by the other recording and reproducing apparatus, in a simultaneous manner. In a case where the VTR is of the helical scan system, the recording signal is successively recorded on a plurality of parallel tracks which are formed in an oblique manner with respect to the longitudinal direction of the magnetic tape. Each block of the recording signal is recorded in each track. Upon reproduction, the two recording and reproducng apparatuses are synchronously operated by use of the synchronizing signal. Moreover, the timing of the magnetic tape travel between both apparatuses is adjusted, so that the address signals of the reproduced signals obtained from the two apparatuses respectively coincide.
In order to adjust the timing of the magnetic tape travel between both apparatuses during the above reproduction, the tape travel of one recording and reproducing apparatus is temporarily stopped at the point in time when a specific address signal is reproduced, while the magnetic tape travel in the other recording and reproducing apparatus is not stopped until the same specific address signal as that above is reproduced. When the same specific address signal is reproduced in the above other recording and reproducing apparatus, the magnetic tape travel is temporarily stopped, and then, the magnetic tape travel in both recording and reproducing apparatuses are started simultaneously.
However, even when the address signal is detected as described above to stop the magnetic tape travel, the magnetic tape travel actually cannot be stopped immediately due to mechanical causes in the magnetic tape moving system. Accordingly, the magnetic tapes in both recording and reproducing apparatuses do not stop at completely identical positions, and shifts of over several tracks are introduced with respect to the corresponding tracks. Hence, even when the magnetic tape travel in both recording and reproducing apparatuses are started simultaneously, the blocks having the same address are not reproduced simultaneously, although the beginnings of the data blocks are reproduced together. Therefore, shifts of over several blocks in units of blocks are accordingly introduced, and a so-called synchronous error is introduced.
When the above kind of shift (error) exists, the reproduction fidelity becomes low and degradation is introduced in the sound quality.
Thus, a system can be considered in which the tape travel of one recording and reproducing apparatus is controlled while the tapes are travelling, after the tape travel in both recording and reproducing apparatuses are started simultaneously. The timing of the tape travel between both recording and reproducing apparatus can be adjusted so that the reproduced address signals from both apparatuses coincide, by the control operation performed with respect to the above one recording and reproducing apparatus. However, even when the tape travel is controlled after the tape travel is started to initiate reproduction, time is required until the addresses of both tapes perfectly coincide and the phases of the reproduced blocks perfectly coincide. Hence, there is a disadvantage in this system in that it is inevitable for degradation to be introduced in the sound quality of the reproduced sound. Therefore, the above system is not suited for practical use since a reproduced sound having a fine sound quality cannot be obtained immediately.